Method of forming a hollow box in a metal wall



NOV. 25, A.HU ET I 2,861,335

METHOD OF FORMING A HOLLOW BOX IN A METAL WALL Filed Jan. 4, 1955 2 Sheets-Sheet 2 atent METHOD OF FORMING A HOLLOW BOX IN A METAL WALL Andi- Huet, Paris, France Application January 4, 1955, Serial No. 479,737 Claims priority, application France February 26, 1954 3 Claims. (Cl. 29-545) The present invention relates to the'forming of hollow bosses or nipples, or flanged openings in metal walls, and has for an object to provide an improved method, and apparatus for forming such nipples in metal walls.

It has already been proposed to produce hollow bosses in a plane or cylindrical metal wall by means of a punch which is pushed through the suitably heated metal wall from one side thereof and presses the metal of the wall into a clearance space between said punch and a die held against the other side of the Wall.

Hollow bosses produced in this wall may be slightly irregular and are in general not suitable for directly welding a connecting tube on to the edge of the boss, and a further machining operation is usually required before the tube can be welded on to the boss.

The present invention provides a method for producing, if desired in a single operation, a finished hollow boss that does not require any machining to enable a connecting pipe to be Welded on to it.

According to the present invention the inside of the die is heated during the punching operation whereby the metal is maintained at a suitable temperature during the working stroke of the punch. In this manner, drawing of the metal is avoided and a hollow boss with a tapering lip, i. e. diverging further from the wall, is obtained, and since the metal is forced as far as it will go into a clearance space between the punch and the die, the edge of the hollow bossformed by the pressing of the metal against the bottom of the diecan be conveniently chamfered by the bottom of the die, so that a connecting tube can be welded directly on to the hollow boss without requiring any prior machining operation on the boss.

In the case for example of a superheater header, there may not be snfiicient space inside the header to receive a punch of a length such as has been described above. The hollow boss can then be produced in two stages, the first stage with the use of a punch of conventional type which roughens out the hollow boss, and the second stage with the use of a follow-on punch consisting of a cylindrical collar followed by a truncated-cone or curved portion, which presses against the inside of the roughedout boss.

The following description, given by way of an example with reference to the accompanying drawings, illustrates one manner in which the present invention can be carried into effect.

In the drawings: I

, Fig. 1 is a section through the wall of a superheater header in which a hollow boss is to be formed and showing a punch and jack on the inside of the wall and adie on theoutside of the wall, the parts being shown in position before the commencement of the punching operation.

Fig. 2 is a sectional detail view of the punch head engaged in the wall of the superheater header, during the process of toughening-out the hollow boss.

Fig. 3 shows the punch in position at the end of the operation, after having traversed the wall and after hav- "Patented Nov. 25, 1958 .2 ing produced in a single operation a hollow boss in its finished shape.

Figs. 4 to 7 represent a modification of the method of the invention in which two punches are used consecutively, viz:

Fig. 4 shows a conventional ersed the superheater header hollow boss. I I I V Fig. 5 shows the beginning of the finishing operation, by which a follow-on punch produces the finished shape of the boss.

Fig. 6 is a variant of Fig. 5, and

Fig. 7 shows the finished hollow boss formed working stroke of the follow-on punch. 7

Referring to Figures 1 to 3 of the drawings, there is inserted in known manner inside a superheater header, a portion of the wall of which is shown at a, a jack b which carries a punch c. The jack is positioned opposite a hole a which is drilled in the wall desired to form a hollow boss.

On the other side of the wall a there is placed a die d which is shaped as at e to give the outside of the hollow boss its finished Shape. The die d has a recess I extending from the bottom of the die.

The punch c comprises a head g of conventional type (either pointed or conical) which is adapted to traverse the metal wall a and form the edge of the hollow boss. Following the head g there is a cylindrical collar h, (for the purpose hereinafter described) and then a truncatedcone or curved base portion i which, as will be described, effects the final pressing of the metal into the die.

In the recess of the die d there is provided a guide pin j positioned axially of the die and which is adapted'to engage in a mating axial bore k in the punch, whereby the punch is guide towards the end of its working stroke, as will be hereinafter described.

In the die a there are provided channels d introduction of hot gases produced for exampleby a burner, and escape channels d for the said gases. This construction enables the metal to be kept hot during the boss-forming operation.

This heating, which renders the ductile, may render unnecessary the at the end of its working stroke by pin j.

Thus, after the area of the wall a in which it is desired to produce the hollow boss has been first heated to the desired temperature, and the punch-and-die set has been placed imposition as shown in Fig. 1, the jack forces the punch into engagement with the wall and the head g traverses the wall, producing the edges of the hollow boss 1 so that, as shown in Fig. 2

which has not punch after having travwall and roughed-out a by the for the metal wall a more guiding of the punch means of the guide to the known manner of forming a hollow boss. a To form directly the hollow boss in its finished shape, the working stroke of the punch c islengthened, that is The bottom of the a at the place where it is is at the level of the protruding edge portion of the hollow boss so that the internal surface of the boss at the said level is made cylindrical and is suitable for the subsequent application of a welding ring for welding a q ass ius p p on to he cha r d n m .of he oss:

At the end of the compression of the metal there may be present an excess of metal in the form of chips cut by the upper, more or less sharp edge of the cylindrical collar h or by the edges of notches (not shown) provided in the periphery. of the collar. Such chips collect in the space between the punch head g and the recess 1 in the bottom of the die; to remove such chips after such operation, there may be provided in the bottom of the die a removal device in the form of a double-bottom extractor.

It will be observed that in the known arrangements the punch is guided towards the end of its working stroke only by the guiding of the punch-carrying piston 11 in the cylinder of the jack [2. In the, present case of'the lengthened stroke of the punch it may prove necessary to make the alignment between punch and die positive by providing guiding means for the head of the punch. This guidance is obtained by means of the guide pin 1' which enters the bore k in the punch. In this manner reliable centering between the punch head and the punch itself is achieved towards the end of the stroke of the punch. Afterwards, the circular collar h enters the recess of the die and so assists this centering.

During the operation of forming the hollow boss, hot gases are introduced into the die if through the channels 21 for heating the metal. appropriate temperature by this means, it is not absolutely necessary to guide the punch head, and the guide pin i can be dispensed with.

The heating of the interior ofthe die'can be turned on automatically when the die is placed in position or when the punch begins its working stroke, and be automatically switched 'off as soon as the hollow boss is completed.

Cooling means (not shown), which may comprise channels through which a coolant is caused to flow, may be provided to cool the punch and the die when required.

The-use of a punch as shown in Figs. 1 to 3, which is longer than the conventional punch, and has a lengthened working stroke, may not always be possible as in the case for example in which the superheater header is too narrow to permit the insertion therein of, such a punch together with its jack. In such a case a two-stage operation may be carried out. In the first stage, performed with a conventional punch as shown in Fig. 4, a rough boss-l (Fig. 4) is formed; the conventional punch is then replaced by a further punch having a head formed by a cylindrical collar h followed by a conical base porthan i (which is wider than the conventional punch 'first used) as shown in Fig. 5.. After the hollow boss has been heated again (preferably internally) the further punch is forced from the position shown in Fig. 5 to the position shown in Fig. 7 and, as in the previous case, thereby compresses the metal in the regions A and B and causes it to flow into the bottomof the die d. During the follow-onoperation represented by Figs. 5 and 7, the interior of the die can be heated as in thecase of the operation described with reference to Figs. 1 to 3.

Instead of producing a single chamfer m on the edge of the hollowboss, a double chamfer may be formed, and in this case the bottom of theidie d is undercut to form a small stepn (Fig. 6) which causes the formation of a second chamfer on the edge of the boss of opposite slope to the first. The provision of'such a double chamfer makes it easier to place thewelding ring .on, the lip of the finished boss. I

If the metal is heated to an What I claim is 5 1. In a method for forming a hollow boss in a plane or cylindrical metal wall by means of a punch which penetrates from one side of the wall and squeezes the metal into a clearance space between the punch and a die held against the other side of the wall, the steps which comprise preheating the wall before the punch is actuated and, during the punching operation continuously heating the portion of the wall disposed within the die by means i. of heated gases by providing within the die a confined heating chamber containing said gases and communicating with said portion of the wall within the die, the heated gases being prevented from leaving said chamber except through confined outlet channels, whereby said a confined chamber is filled with said hot gases at all times.

2. A method of forming a hollow boss in a plane or cylindrical metal wall by means of a punch which penetrates from one side of the wall and squeezes the metal into a clearance space between thepunch and a die held against the other side of the wall, the steps which comprise preheating the wall before the punch is actuated and, during the punchingv operation continuously heating the portion of the wall disposed within the die by means of heated gases by providing within the die a confined heating chamber containing said gases and communicating with said portion of the wall within the die, the heated gases being prevented from leaving said chamber except through confined outlet channels, whereby said confined chamber is filled with said hot gases at all times, and efiecting an elongation of the working stroke of the punch to permit the use of a punch having a truncatedcone or curved base which compresses into the bottom of the die the metal of the roughed out hollow boss formed at the beginning of the punching operation, the bottom of the die being shaped so as to impart the desired finished external shape to the hollow boss.

3. A method of forming a hollow boss in a plane or cylindrical metal wall by means of a punch which penetrates from one side of the wall and squeezes the metal into a clearance space between the punch and a die held against the other side of the wall, the steps which comprise preheating the wall before the punch is actuated and, during the punching operation continuously heating the portion of the wall disposed within the die by means of heated gases by providing within the die a confined heating chamber containing said gases and communicating with said portion of the Wall withinthe die, the heated gases being preventedfrom leaving said chamber except through confined outlet channels, whereby said confined chamber is filled with said hot gases at all times, and effecting a follow-on operation carried out by means of a follow-on punch having a truncated cone or curved base which is wider than the first punch used and which compresses the metal of the roughed-out boss formed by said first punch, into the bottom of the die, the said bottom being shaped so as to impart the desired finished external shape to the hollow boss.

References Cited in the file of this patent UNITED STATES PATENTS Russell Dec. 13, Thackray Mar. 3, Rode July 19, Sherman May 9, Bayer Dec. 22, Lowery -Q. Apr. 17, Ebbetts Aug. 14, Williams -Q July 29, Schwartz Nov. 16, 

